Genotype effect of South African barley cultivars on malting quality under different nitrogen levels
The genotype effect of South African barley cultivars on malting quality under different nitrogen applications was determined by planting two- and six-row doubled haploid populations consisting of 7 and 67 lines respectively under irrigation at Vaalharts in 2006 and 2007 and at Rietriver in 2007. Three different nitrogen (N) treatments were applied to correlate the amount of leaf N to N in the kernel to implement a practical N fertilizer management system to obtain good malting quality. For treatment one, all of the fertilizer (110 kg/ha) was applied at planting. For treatments two and three, half of the fertilizer (55 kg/ha) was applied at planting while the other half (55 kg/ha) was applied at the sixleaf stage or when 50% of flag leaves were visible respectively. The best N application for the two-row population was treatment three compared to the six-row population which responded differently to all the N applications over years and localities. This study indicated that a practical N fertilizer strategy should include half the N application at planting (55kg/ha) for crop and tiller development and a split application of the other 55 kg/ha at six-leaf and flag leaf stage to enhance kernel plumpness, germination, absorption and yield and maintain optimum kernel N for good malting quality. Timing of N application had a significant effect on all the malting quality traits. However, RP-HPLC results of hordein fractions showed that there was no change in the composition of hordeins in response to timing of N application and to the environment. The two- and sixrow entries within a doubled haploid population differed in malting quality across environments. Genotypes contributed more to variation in a population than the environment for both kernel plumpness and yield. However, for kernel N, the environment contributed more to variation than the genotypes. There were significant correlations between malting quality traits and hordein fractions. In particular, the negative correlation between kernel plumpness and total hordein content at treatment two. Total hordein content forms the majority of total kernel N content and plumpness is known to be associated with low kernel N content. The different barley genotypes were identified by their distinct hordein patterns with RP-HPLC. The C and B hordeins were able to distinguish between two- and six-row genotypes. Averaged across all N treatments, kernel N and protein content was positively correlated with the D:B hordein ratio and negatively correlated with the B:C hordein ratio which indicates that malting quality was reduced.